Organic Light Emitting Diode (OLED) is an organic thin film electroluminescent device, and it has the advantages of simple fabrication process, low cost, high light-emitting efficiency, easy to form a flexible structure and so on. Thus, the OLED-based display technology has become an important display technology.
As shown in FIG. 1, an organic emitting-material diode includes a cathode layer 2, an anode layer 1 and an organic functional layer sandwiched in between the cathode layer 2 and the anode layer 1. The organic functional layer includes an emitting-material layer (EML) 3, an electron injection layer (EIL) 5 and an electron transport layer (ETL) 7 formed between the emitting-material layer 3 and the cathode layer 2, and a hole transport layer (HTL) 4 and a hole injection layer (HIL) 6 formed between the organic emitting-material layer 3 and the anode layer 1.
The light-emitting mechanism for the above OLED is: when a voltage is applied between the anode layer 1 and the cathode layer 2, driven by the external voltage, the holes injected from the anode layer 1 enter the emitting-material layer 3 through the hole transport layer 4 and the hole injection layer 6, and the electrons injected from the cathode layer 2 enter the emitting-material layer 3 through the electron transport layer 5 and the electron injection layer 7. After entering the emitting-material layer 3, the holes and the electrons are recombined to form excitons in the combination area. And the light-emitting phenomenon happen during exciton's radioactive transition is defined as electroluminescence.
Since the light is emitted by the emitting-material layer in random directions, some of the light may be emitted to the opposite direction of the light emission direction of the organic electroluminescent device. In existing technologies, this part of light is simply reflected by the reflective cathode layer 2. Since this part of light travels through other film layers before reaching the reflective cathode layer 2, the light intensity is reduced or attenuated by the other layers, thereby lowering the light-emitting efficiency of the organic electroluminescent device.
The disclosed devices are directed to at least partially solve one or more problems set forth above and other problems, such as how to increase the light-emitting efficiency of the organic electroluminescent device.